The invention relates to a method of forming a servo pattern on a rigid magnetic recording disk, and more particularly to contacting the recording disk with a magnetic pattern on a master disk and transferring the pattern to the recording disk.
In magnetic recording hard disk drives, the conventional method of generating the fixed, pre-recorded servo patterns that are used to position the recording head to the desired track and record location on the disk, is by xe2x80x9cservo-writingxe2x80x9d the patterns on a track by track basis, either with a special write head and servo-writer or with the production head in the drive. This is a time-consuming and therefore expensive process. Contact magnetic duplication or transfer, sometimes referred to as magnetic printing, is a method of instantaneous recording of magnetic transitions or patterns onto magnetic media over large areas and has been proposed for transferring servo patterns to magnetic recording disks in hard disk drives. The contact magnetic transfer method uses a xe2x80x9cmasterxe2x80x9d disk with a pattern of soft (low-coercivity) magnetic material corresponding to the servo pattern which is to be transferred to the magnetic recording disk (the xe2x80x9cslavexe2x80x9d disk). As shown in FIGS. 1A-1B, the slave disk is first DC magnetized or xe2x80x9cerasedxe2x80x9d with a magnet 1 that applies an in-plane horizontal (longitudinal) magnetic field in first direction 2 across a gap 3 between the magnet""s poles, as shown in FIG. 1A. A rigid master disk supported on a carrier is then pressed into contact with the DC-erased slave disk, and a second horizontal DC magnetic field is applied by magnet 1 in the direction 4 opposite to the direction 2 of the first DC magnetization. This produces a magnetization pattern on the slave disk because the first magnetization on the slave disk is shielded from the second DC field in the regions where the islands 5 of soft magnetic material of the master disk are present, and the first magnetization on the slave disk is reversed in the regions beneath the openings 6 in the pattern (the regions between the soft magnetic material on the master disk), as shown by arrows 7 in FIG. 1B. The magnetic field applied to the slave disk beneath the openings 6 is enhanced by the dipole fields 8 in the soft magnetic regions adjacent the openings 6, because in the presence of the field from the magnet these regions generate their own fields.
Contact magnetic transfer was first proposed for generating servo patterns in magnetic recording media in IBM""s U.S. Pat. No. 3,869,711. The ""711 patent is directed primarily to transferring servo patterns to flexible tape from a rigid master drum or to flexible disks from a rigid master disk, but suggests that the master disk may be xe2x80x9cflexiblexe2x80x9d and the slave disk xe2x80x9crigidxe2x80x9d. More recently, contact magnetic transfer and the readback properties of the transferred or printed servo patterns have been studied by Sugita, R. et al., xe2x80x9cA novel magnetic contact duplication technique for servo-writing on magnetic disksxe2x80x9d, IEEE Transactions on Magnetics, Vol 36 Issue 5 Part 1, September 2000, pp 2285-2287; Nishikawa, M. et al., xe2x80x9cReadback properties of novel magnetic contact duplication of high recording density floppy diskxe2x80x9d, IEEE Transactions on Magnetics, Vol 36 Issue 5 Part 1, September 2000, pp 2288-2290; Ishida, T. et al., xe2x80x9cPrinted Media technology for an effective and inexpensive servo track writing of HDDsxe2x80x9d, IEEE Transactions on Magnetics, Vol 37 Issue 4 Part 1, July 2001, pp 1875-1877; and Saito, A. et al., xe2x80x9cOptimization of a magnetic printing process by computer simulationxe2x80x9d, IEEE Transactions on Magnetics, Vol 37 Issue 4 Part 1, July 2001, pp. 1389-1392.
One of the most challenging problems in contact magnetic transfer is achieving the precise level of contact or close proximity between the master and slave disks. If the master and slave disks are too far apart, the servo patterns will not be reliably reproduced. If they are pressed together with excessive force, one or the other may be damaged or the master disk may wear out too quickly, thereby increasing the cost of the servo patterning process. This problem is further complicated because the surface of a typical hard disk to be patterned is not perfectly flat, but exhibits asperities and a curvature that can vary over a relatively wide range. Moreover, the curvature can vary considerably from disk to disk.
What is needed is a method for contact magnetic transfer of servo patterns to hard magnetic recording disks that is reliable, does not damage the disks, and allows for patterning of a large number of disks from a single master disk.
The invention is a contact magnetic transfer method for forming a pattern of magnetized servo regions in the magnetic recording layer of a rigid magnetic recording disk that uses a flexible master disk and a differential gas pressure to press the patterns of the master disk against the slave disk. The master disk is a flexible plastic film with islands of magnetic shielding material extending above the film surface, the islands forming a pattern representative of the servo pattern to be formed in the recording layer of the disk. The plastic film is sealed at the outer periphery of the opening of a pressure chamber with the islands located outside the chamber. The previously DC-magnetized slave disk is brought into gentle contact with the islands and gas pressure inside the chamber is increased to slightly above atmospheric. This controlled pressure presses the islands into contact with the slave disk, at which time a magnet magnetizes the regions of the recording layer of the slave disk that are not aligned with the islands in the direction opposite to the original DC-magnetized direction. The magnet is located on a rotatable stage within the chamber beneath the plastic film and mounted so that the length of its gap is in the radial direction corresponding to the radius of the slave disk.
For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying figures.